Process for the production of acrylic acid from propylene

ABSTRACT

A vapor phase method of oxidizing alpha mono-olefinic hydrocarbon to the corresponding alpha beta unsaturated monocarboxylic acid in a single stage. The process is characterized by the use of a bismuth promoted cobalt-molybdate catalyst having a gram atom ratio of bismuth to molybdenum of from 0.05 to 0.15 and a cobalt to bismuth ratio in the range of 5:1 to 20:1.

United States Patent Inventors R. Parthnsarthy Takoma Park; Robert M. Dobres, Silver Spring; John L. War-then, Baltimore, all 01' Md. Appl. No. 482,487 Filed Aug. 25, 1965 Patented Nov. 30, 1971 Assignee W. R. Grace 8; Co.

New York, N.Y.

PROCESS FOR THE PRODUCTION OF ACRYLIC ACID FROM PROPYLENE 1 Claim, 1 Drawing Fig.

U.S. Cl 260/533 N, 260/530 N, 260/604 R, 252/470 Int. Cl C07c 57/04 Field of Search 260/533, 604

[56] References Cited UNITED STATES PATENTS 3,372,128 3/1968 Maeda et a1. 260/604 3,177,257 4/1965 Detling et al. 260/604 FOREIGN PATENTS 878,802 10/1961 Great Britain 260/530 U 999,836 7/1965 Great Britain 260/5 30 U 903,034 8/1962 Great Britain 260/533 Primary Examiner.lames A. Patten Assistant ExaminerRichard Kelly Attorneys-.loseph P. Nigon and Kenneth E. Prince ABSTRACT: A vapor phase method of oxidizing alpha monoolefinic hydrocarbon to the corresponding alpha beta unsaturated monocarboxylic acid in a single stage. The process is characterized by the use of a bismuth promoted cobalt-molybdate catalyst having a gram atom ratio of bismuth to molybdenum of from 0.05 to 0.15 and a cobalt to bismuth ratio in the range of5:1 to 20:1.

PROCESS FOR THE PRODUCTION OF ACRYLIC ACID FROM PROPYLENE This invention relates to an improved process for the production of alpha beta unsaturated oxygen containing compounds comprising aliphatic monocarboxylic acids. More particularly, the invention relates to an improved process for the direct vapor phase oxidation of propylene and/or isobutylene to acrylic acid and/or methacrylic acid respectively.

The aliphatic monocarboxylic acids having alpha, beta unsaturation, such as acrylic acid and methacrylic acid, for example, are valuable starting and intermediate materials for a whole series of reactions because of their highly reactive nature. However, their reactive nature also makes these materials difficult to prepare and contributes to the problems encountered in large scale production of these acids.

The prior art processes for the production of acrylic acid and/or methacrylic acid have been based on operational procedures which are complex and costly and which do not lend themselves to economical large scale operation. These procedures generally comprise liquid phase operations which of necessity require relatively costly equipment and are very difficult to control.

It has been recognized for some time that a potential source of the alpha, beta unsaturated acid is their corresponding olefins. However, large scale production of the acids from this group has not followed because of the relatively low yields and costly operational steps involved in the available processes.

The prior art processes generally resulted in the preparation of a mixed product that contained substantial amounts of the alpha, beta unsaturated aldehydes and very little or no alpha, beta unsaturated monocarboxylic acids. These processes were frequently directed to utilization of the aldehydes in the subsequent preparation of monocarboxylic acids. Procedures of this type was obviously cumbersome and commercially unattractive.

We have found that although the use of a cobalt-molybdate catalyst in the vapor phase oxidation of olefms to unsaturated carboxylic acids, particularly the vapor phase oxidative conversion of propylene and/or isobutylene to acrylic acid and/or methacrylic acid, did not result in a substantial conversion, the promotion of this catalyst with a small but significantly important amount of bismuth results in a greatly improved yield of the unsaturated monocarboxylic acid product. Thus we have found that bismuth promoted cobalt-molybdate catalyst containing a small but critical amount of bismuth results in a selective conversion of propylene to acrylic acid, whereas the presence of bismuth in higher amounts results in products containing no appreciable amount of unsaturated acid.

The hydrocarbon raw material used in the process of our invention can be broadly defined as olefinic unsaturated hydrocarbons. This invention is particularly applicable to normal gaseous hydrocarbons comprising propylene and/or isobutylene. Propylene is converted to reaction products comprising substantial amounts of acrylic acid and isobutylene to substantial amounts of methacrylic acid.

It is not necessary that the olefin be purified. The raw material for use in our process may contain other hydrocarbons in the vapor state which do not undergo substantial reactions but which do not adversely affect the oxidation under the conditions of our process. Thus, the feedstocks of our process may contain in addition to unsaturated olefinic hydrocarbons such as propylene and isobutylene, for example, other parafinic hydrocarbons such as methane, ethane, butanes which are in a vapor state under the conditions of operation of the claimed process.

ln accordance with our process, the olefin contained charge is admixed with added oxygen in the form of an oxygen contained gas or oxygen in relatively pure form is passed through a reaction zone containing our novel catalyst.

The oxygen for use in this process may be recovered from the fractionization of air or it may be a more dilute oxygen containing gas. A suitable source of oxygen comprises, for example, molecular oxygen in admixture with an inert diluent gas such as nitrogen. Air may be used as the source of molecular oxygen reactant. The oxygen containing charge'may be admixed with the olefinic charge of the system before it is introduced into the reaction zone, but may be introduced in part or in its entirety directly into the reaction at one or more points in the reaction zone. Once the reactants are passed into the reaction zone, they are contacted with the catalyst.

In investigating catalysts for this reaction, we have found co-precipitated cobalt-molybdate catalyst promoted with bismuth to be highly selective. Freshly precipitated cobaltmolybdate alone is too active in that it converts 27 percent of the propylene at a temperature of 660 F. The unpromoted catalyst was 34 percent selective to acetic acid, 52 percent to carbon oxides and only '10 percent to acrylic acid. Thermal treatment deactivated the catalyst and improved the acrylic acid selectively to 34 percent at the expense of the acetic acid which was then reduced to 13 percent;

However, introducing a small amount of the bismuth promoter in the preparation of cobalt-molybdate catalyst shifted the selectivity to acrylic acid and acrolein at the expense of the acetic acid. The coprecipitated cobalt-bismuthmolybdate catalyst converted 35 percent of the propylene charge and was 48 percent selective to acrylic acid, 20 percent to acrolein and only 14 percent to acetic acid.

Our process is carried out at temperatures in the range of 700 to 950 F., preferably at 750 to 850 F. The propylene is present in an amount equal to 2 to 20 volume percent, preferably 4 to 12 volume percent of the reaction mixture. The ratio of oxygen to propylene is maintained in the range of 0.5 to l to 5 to l. The preferred oxygen to olefin ratio is l to l. The reaction is carried on for a period of time such that the reactants contact the catalyst for periods of l to 10 seconds, preferably about 3 to 4 seconds.

Alpha mono-olefinic hydrocarbons containing fewer than eight carbon atoms in the molecule can be converted, according to our process, to a reactant mixture comprising substantial amounts of alpha beta unsaturated monocarboxylic acid corresponding to said olefinic hydrocarbons by reacting said olefinic hydrocarbons in a vapor phase with an oxygen containing gas at a temperature of about 700 to 900 F. in a bed of a catalyst consisting of a bismuth promoted cobalt-molyb date wherein the gram atom of bismuth to gram atom of molybdenum ratio is in the range of 0.05 to 0.l5 and wherein the bismuth promoter in the cobalt-bismuth-molybdate catalyst is present in a cobalt to bismuth ratio in the range of 5 to l-20 to l..Air can be used as the oxygen-containing gas.

The bismuth promoted cobalt-molybdate catalyst employed in the process of this invention may be prepared by physically mixing bismuth molybdate with the cobalt-molybdate catalyst prepared in the usual manner. In the preferred process coprecipitation of the two molybdates is achieved when a bismuth solution is added to the cobalt solution and this mixture of salts is treated with ammonium molybdate solution. The precipitation is completed by adjustment of the pH. The resulting mixture is then dried, pilled if desired, and calcined.

The mole ratio of cobalt to bismuth in the catalyst should be in the range of5zl to 20:1.

The preferred catalyst contains a cobalt to bismuth ratio of 9 to l. The amount of bismuth present in the catalyst is critically important. Optimum yields of acrylic acid are obtained when the gram atom of bismuth to gram atom of molybdenum ratio in the catalyst is in the range of 0.05 to 0.15. lncreasing the bismuth content of the catalyst to a cobalt to bismuth ratio of 4 to l shifts its selectively more towards acrolein. The concentration of molybdate should also be controlled so that the M00 to cobalt plus bismuth ratio is at least 1.0.

The criticality of the bismuth concentration is shown in the FIGURE. The FIGURE shows that the alpha beta unsaturated acid of the product goes through a maximum at gram atom of bismuth to gram atom molybdenum content of about 0.1. lncreasing this ratio to the order of 0.2 results in a drastic increase in the amount of acrolein recovered from the reaction. The acetic acrid recovery decreases progressively with increase in the bismuth content of the catalyst. lt is apparent from the examples and the graph that the products of a once A The invention is further illustrated by the following specific but nonlimiting examples.

EXAMPLE I This example describes the preferred method of preparing our bismuth promoted cobalt-molybdate catalyst.

To 265 grams of cobalt nitrate, Co(No,),-b6l-i,0, dissolved in 250 ml. of deionized water, was added a solution of 38.5

4 EXAMPLE III A mixture of propylene air and steam containing a volume percent ratio of propylene to oxygen and steam of 7.5 to 37.5

to 55 was passed through a bed of a cobalt-molybdate-bismuth catalyst having a cobalt to bismuth ratio of 9 to l. The system was operated at a temperature of 798 F. and a pressure of one atmosphere. The contact time was 3.6 seconds. The reactor effluent was recovered and analyzed. The propylene conversion was 35 percent with a selectivity to acrylic acid of 48.4 percent and to acrolein of 20.2 percent. The selectivity for acetic acid was l5.7 percent and for acetalaldehyde, 1.6 percent. The amount of converted propylene going to carbon oxides was 15.6 percent.

grams of bismuth nitrate Bi( Mo h-511,0 in 50 ml. of deionized water and 10 ml. of 25 percent nitric acid. The mixture was EX M E v maintained at a temperature of 140 F. A charge of 177 grams of ammonium molybdate, (NR4) 40202441420, was dissolved The cnticality of the cobalt-bismuth ratio in the cobaltin 200 ml. of deionized water. The solution was heated to 140 bismuth'mlybdae caalyst er"P"asized a Whih The ammonium molybdate Solution was added to the the cobalt-bismuth ratio in the catalyst 4 to l. in this run, cobalt-bismuth solution with stirring. The temperature was a f of Propylene" and steam m a volumc Pe'ccm maintained at 140 F. during this addition. The mixture "3 of7-5 to 315m 55 were passed through a bed ofcobaltthickened upon addition of the molybdate. The pH of mixture bsmuthmolybdafe catalyst h'avmg a cobalt to blsmmh of was adjusted by adding 182 of 50 percent ammonium 4 to l. The reaction was carried out at a temperature of 870 hydroxide solution dropwise with stirring The final PH was F. The contact time was 3.6 seconds. The reactor effluent was 6.2. The mixture was stirred an additional 15 minutes, filtered recovered and analyzed' A total of 26 Pcrcem of the and washed with 2 liters of deionized water. The filtrate was Propylene was convenFd i a selcctivity acrolein of checked by adding additional ammonium hydroxide to be sure Percem and W and of P only that precipitation was complete. The products were dried for P m aceilc and fcetalalfjchyde were refovefed m 40 hours at 220 F. and calcined for l6 hours at 1000 F. The P'" m product was sized to recover those particles in the 8 to 25 vened P w was Percentmesh size range. The ratios of components in the products EXAMPLE,

were as follows:

. The criticality of the bismuth promoter was shown by passing the mixture of propylene, air and steam to the reactor in the presence of a fresh and deactivated cobalt-molybdate cabal 09 catalyst. The data showing feed temperature, conversion, coni h tact time, propylene conversion and selectivity of the convermolybdenum 1. sion is set out in table 1 below:

TABLE I Selectivity oi conv. in percent percent F. time, conv., Acrylic Acetic Acet- Carbon Catalyst C|=8ll'-H:O avg. bed sec. percent Acrolein acid acid aldehyde oxide Fresh CoMoO, (It-e473) 5-50-45 660 3.6 27 0. 3 0. 33.8 0. 3 52.4

CoMoO; deactivated at 1,200 F 10-50-40 803 3.0 20 0.5 34.4 12.5 40.3

(Jo-Bi molybdate (CozBi 4:1) 7. H7. 5-55 870 3.6 20 51.5 10.5 (J 23.9

Co-Bl molybdate (CmBl 9:1) 7. 5-37. 5-55 798 3.5 35 20. 2 48.4 15.7 1.5 15.6

Only minor amounts of acetic acid and aceteldehyde were recovered in the reaction.

EXAMPLE ll A catalyst was prepared to contain a cobalt/bismuth/molybdenum ratio of 0.8 to 0.2 to l. in this preparation, 233 grams of cobalt nitrate was dissolved in 220 ml. of deionized water and heated to l40 F. The bismuth solution was prepared by dissolving 97.6 grams of bismuth nitrate pentahydrate in I00 ml. of deionized water and 20 ml. of 25 percent nitric acid. The bismuth solution was added to the cobalt solution with stirring while maintaining the temperature at 140 F. A solution of ammonium molybdate was prepared by dissolving l77 grams of the salt containing four molecules of water in 200 ml. of deionized water. The solution was added to the cobaltbismuth solution with strong stirring. The temperature was maintained at l40 F. The mixture thickened to the extent that it was necessary to add 500 ml. of deionized water in order to facilitate stirring. While the mixture was being stirred, 230 ml. of a percent ammonium hydroxide solution was added. This addition adjusted the pH of the mixture to 6.4. The mixture was filtered and washed with 2 liters of deionized water and dried 40 hours at 220 F. The product was calcined for 16 hours at 100 F. and sized to recover the product in the 8 to 25 mesh size range. The yield in the reaction was 85 percent.

it is apparent from review of these data that the bismuth propylene conversion increased to 35 percent with the acrylic acid conversion increasing to 48.7 percent. The use of the cobalt-bismuth-molybdate catalyst also resulted in a reduction of the carbon oxide selectivity of the conversion to 15.6 percent.

When we use the term selectivity" to acrylic acid and to acrolein based on propylene charge, we means the number of moles of acrylic acid and acrolein respectively produced, multiplied by 100, divided by the number of moles of propylene in the charge converted.

Obviously many modifications and variations of the invention may be made without departing from the essence and scope thereof and only such limitations should be applied as are indicated in the appended claims.

What is claimed is:

1. A process for the production of acrylic acid which comratio in the catalyst is about of 0.05 to 0.15 and wherein the cobalt to bismuth mole ratio in the catalyst is in the range of [5: 1-20: I of bismuth to gram atom of molybdenum ratio is in the range of 0.05 to 0.15.

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